Initially

Initially is a Minecraft modification that automatically populates the player's inventory with a pre-configured set of items upon first entering a world.

In the JSON configuration file, you can specify exactly which items should be placed in each inventory slot, as well as set additional data (NBT tags) for each item if needed.

To get the NBT data of a specific item, hold it in your hand and execute the command /data get entity @s SelectedItem. Copy the identifier and specify it in the itemLocation parameter, then remove it from the tag—do the same with the count.

Important! Before adding to JSON, you must escape all nested strings (you can use specialized online tools for this).